Is it possible to redirect using a POST method ?
Or should redirects always be made using GET ?
The use for this is in the final steps of an order process for an e-commerce site, to send the data to the payment processor, without introducing an extra step for the user.
Redirection isn't possible with POST requests - it's part of the HTTP/1.1 protocol.
You could either introduce another step that contains the form data to be POSTed to the payment processor, or you could send the post from your application (something I have done when working with PROTX).
I "solved" the issue by displaying a summary page with all the products and delivery charges etc, with the typical "to confirm and pay for your purchases, click the continue button below" type message. The continue button causes the site to POST the product data and everything across to the payment processor.
The short answer - there is another step for the user. However, the key is to make it seem as natural and as much part of the checkout experience as you can. This way, it doesn't come across too much as "just another step".
However, if you do come across a better way, I'll be very interested to hear what it was :)
With a simple line of javascript, you can have your POST form to post itself (form.submit()). You can then hide the form and display a simple "please wait while..." message to the user while the form is submitted to the payment processor.